The majority of carburetors used for supplying controlled ignition automobile engines with air-fuel mixtures comprise a gasoline pump, known as an "enrichment or acceleration pump". The purpose of this pump is to inject a quantity of vaporizable fuel, basically motor spirit, that is predetermined and increasing with the stroke of the accelerator pedal, so that the walls of the air intake pipes leading into the engine are moistened by the fuel and that after a sudden opening of the carburetor, the air-gasoline mixture retains a richness in gasoline close to that of the explosive or stoichiometric mixture. In fact, during complete opening of the carburetor, vaporization of the gasoline occurs not only in the carburetor, but also along the length of the intake pipes moistened by the gasoline in excess and situated downstream from the carburetor.
The action of the enrichment pump of the carburetor is carried out upon each depression of the accelerator pedal by a supplementary injection of gasoline that can reach several cm.sup.3 per stroke according to the types of engines used. Apart from the acceleration phases at low R.P.M., this supplementary gasoline injection is not effective in suppressing a carburation gap. In order to suppress the gasoline consumption provoked by the actuation of the enrichment pump and the risk of cleaning out of the lubricating oil caused by this unburned gasoline injected at each acceleration, it has been proposed to suppress the enrichment pump, or to operate it only for low R.P.M. of the engine, but these dispositions although they are acceptable for drivers who do not require high performances from their engines, always become apparent by carburation deficiencies, in particular, during cold running of the engine and cannot be generalized.
The present invention proposes to suppress the effect of the carburetor enrichment pump at high R.P.M. of the engine while obtaining for the carbureted mixture a lean effect with increases which the engine R.P.M. but the increase of which is less and less rapid, so that the carburation of the mixture is always close to the optima (stoichiometric mixture) and reduces the consumption of the engine while improving its facility to change its R.P.M.